To anchor one end of the safety belt it has been the practice to use a ring which is pivotally attached to a lashing which in turn is non-pivotally attached to the floor of a vehicle or the side wall of a vehicle. For this purpose a number of different ring configurations have been proposed. Many such guides have proved to be inadequate if the belt runs from a belt winder on the floor of the vehicle vertically up to such a guide, then through it and then forward across the chest of the passenger, as shown in the French Pat. No. 1,498,883. If the passenger has an accident, the forward motion of his upper body pulls at the guide which makes the lashing pivot. If the lashing is not pivotally attached, the belt in the ring moves. Directly after this another section of the belt moves through the ring, because the belt roll does not lock immediately when the belt is pulled, but it only locks later after some more belt has been unrolled. In addition, the section of the belt between the guide and the belt winder on the floor of the vehicle is stretched with the result that more belt is pulled through the guide.
Experience has shown that with the familiar guides in the case of an accident the belt is displaced and because of the very high tension the section of the belt which is pulled through the ring is crushed, causing only a section of the belt to stay directly on the ring, unless additional measures are taken. Such wrinkling causes a much greater friction of the belt sections in the ring during an accident -- a friction which does not only exist directly between the belt and the ring itself, but also within the fabric of the belt because of the pressure. Because of a reduced contact area of the belt in the ring and at the same time an increase in the tension of the belt, a considerable pressure develops between belt and ring of the guide. The outer and inner friction leads to a localization of heat in the belt which could cause a damage to or even breaking of the belt. This is true of a tension in the belt which might be considerably lower than that which a belt without wrinkles could tolerate.
German patent application Auglegeschrift No. 1,780,043 endeavored to eliminate this disadvantage and to create a metal guide for safety belts which avoids the wrinkling of the belt in case of an accident, in order to reduce the outer and inner friction of the belt, compared to the familiar metal guides, to a minimum. This was accomplished in German Pat. No. 1,780,043, among other design changes, by making the ratio of the highest height of the opening to the widest width of the opening greater or 1:3 and the transition from the bar of the ring opposite of the lashing to the side bars of the opening with a bend radius which is equal or greater than 0.2 times the height of the opening. Furthermore, the lashing on the vehicle and the ring in the lashing were pivoted in two planes vertically to each other.
The metal guide was provided to move on gimbals and turn in the direction of the tension which occurs in the metal guide during an accident. This reduced the danger of wrinkling, because the pressure on the belt at right angles to its length is only very small.